A device-to-device (D2D) system where communication is performed inside a multi cell system or an ad-Hoc network may include a two-way relay system. In a communication system including this two-way relay (referred to as a ‘two-way relay system’ hereinafter), terminals which are close geographically under a wireless environment transmit/receive a signal via a two-way relay that uses a so-called amplify-and-forward (AF) protocol.
A two-way relay system may improve spectral efficiency about two times compared to a one-way relay system. This performance improvement may be obtained by a process where two terminals transmit information to a relay simultaneously during a first time slot, and the relay transmits the information again to the terminals during a second time slot. At this point, each terminal may cancel self-interference (self-interference cancellation (SIC)) that occurs when a signal transmitted by the terminal itself is received again by way of the relay. However, when using a two-way relay system, relay filter design techniques proposed on the assumption that channel information is accurately known for SIC and relay filter design are mostly used. For example, papers by N. Lee, H. Park, and J. Chun, “Linear precoding and decoder design for two-way AF MIMO relaying system”, Proc. ICC 08, 2008. and G. Li, Y. Wang, and P. Zhang, “Optimal linear MMSE beamforming for two-way multiantenna relay systems”, IEEE Communications Letters, May, 2011 propose methods for repeatedly obtaining a matrix corresponding to a relay filter and SIC on the assumption that channel information is accurately known.
For a two-way relay system to properly operate in an actual system and take effect, how channel information may be estimated and how a relay filter may be designed based on the estimated information are important issues. Paper by G. Wang, F. Gao, Y. -C. Wu, and C. Tellambura, “Joint CFO and channel estimation for OFDM-based two-way relay networks”, IEEE Transactions on Wireless Communications, February, 2011 proposes a channel estimation method for performing SIC successfully under a circumstance where all terminals and a relay have one antenna. However, this channel estimation method is difficult to extend to a system where a plurality of antennas exists. Therefore, a technique for effectively performing SIC via relay filter design and channel estimation, capable of resolving above-described limitations and remarkably improving performance of a two-way relay needs to be proposed.